This application claims priority based upon German Application Ser. No. DE 199 09 620 1, filed Mar. 5, 1999, and PCT/EP00/00807, filed Feb. 1, 2000.
This invention relates to an apparatus for tensioning and closing tightening straps, in particular made of plastics, for tightening packages. This apparatus further includes a closing device for connecting the two ends of the tightening strap and a tensioning device which consists essentially of a tensioning wheel, which can be driven, a pressure plate, which can be moved against the tensioning wheel or lifted therefrom, and a self adjusting separating element, which is arranged between these two parts, whereby one end of the strap is received between the tensioning wheel and the separating element, and the other end of the strap is received between this and the pressure plate.
Such an apparatus serves to provide a package as for example a packed pallet or a large carton with a tightening, and to hold together the goods which are stacked on the pallet or packed into the carton and to secure them for transport. For the production of the tightening, a rigid strap, usually of plastics, is placed around the package, and then the ends of the strap are tensioned against one another with the help of the apparatus and are connected to one another when the desired tension is reached. The connection takes place with the help of the closing device, which consists generally of a friction welding device for plastic straps. The ends of the strap are threaded laterally into the tensioning device for tensioning, whereby the lower end of the strap lies between the pressure plate and the separating element, and the upper second end of the strap lies between the separating element and the tensioning wheel. The tensioning wheel, which is usually provided with barbs at its peripheral surface, or which is roughened in another way, is rotated by means of a suitable drive and draws the upper end of the strap through the apparatus into the closing device which is arranged behind the tensioning device, while the lower end of the strap is held in a clamping manner between the pressure plate and the separating element. The separating element is mounted in the tensioning device in a self-adjusting manner, that is, it can move within certain limits during the tensioning process, and so take up an optimal position relative to the tensioning wheel, so that the friction closure between the tensioning wheel and the upper end of the strap, which is necessary for the tension, is always ensured by means of the automatically resulting best position of the separating element relative to the tensioning wheel. The tightening strap can be pretensioned with a very strong force by means of the self-adjusting xe2x80x9cflyingxe2x80x9d arrangement of the separating element, which is sometimes also called high tension wedge, and it can thereby ensure a very rigid tightening of the package, which is required in particular when transporting heavy packed goods over longer distances.
After the two ends of the strap are tensioned against one another with the desired tensioning force in the described manner, the closing device is actuated, whereby the two ends of the strap are pressed rigidly on top of one another by means of a pressure or a friction plate before they are connected to one another. With plastic straps, the connection usually takes place by means of friction welding, as mentioned, whereby the friction plate moves the upper end of the strap with a high speed transversely to the longitudinal direction of the strap over the lower end of the strap to and fro, and the friction heat resulting therefrom melts the ends of the strap at their surface and welds them to one another in this way. Subsequently, the drive for the to and fro movement of the friction plate is shut down, but this is kept in its lowered position which presses the two ends of the strap together, in which it presses together the ends of the strap, which are under tension, and therewith their load capacity, until the weld connection has cooled down.
After the completion of the tightening in the described manner, the apparatus has to be removed from the package or from the tightening strap. For this, it is necessary to lift not only the pressure plate and the separating element far enough from the tensioning wheel, so as to be able to thread the ends of the strap lying there between laterally out of the apparatus, but first the pressure or the friction plate of the closing device has to be lifted from the two ends of the strap which are connected to one another, as otherwise a lateral threading of the ends of the strap from the apparatus is not possible. In particular with an apparatus, in which the tightening straps are pretensioned with a very strong pretension force, for example with an apparatus which comprises a hydraulic or pneumatic drive for the tensioning wheel, the pressure or friction plate is under a large tension after the connecting or welding of the two ends of the strap, which tension is exerted thereon from the upper end of the strap, which is pretensioned with regard to the lower end of the strap. That is, the pressure or the friction plate is held under tension by the upper end of the strap in the longitudinal direction of the apparatus, which results in that venting or lifting of the friction plate after connecting the ends of the strap is only possible with a large force. It has indeed already occurred with an apparatus, in which the closing device is opened (vented) manually by means of a manual lever, that the force necessary for lifting the pressure plate was so large that the manual lever did not withstand the loads and broke.
So as to ease the opening or venting of the closing device, the tensioning device is usually vented first, that is, the pressure plate and the separating element are lifted a little from the tensioning wheel, with the aim that the two ends of the strap which pass between these three parts will be disengaged from the tensioning wheel, the separating element and the pressure plate, so that the upper end of the strap is no longer under tension, and thereby the pressure or friction plate of the closing device is also relieved. It has been shown that with such an apparatus, in which the ends of the strap are tensioned against one another with a strong force, these do not disengage safely from the tensioning wheel and the pressure plate when venting, but stay at the rough or toothed surface and retain their mutual pretension, so that the pressure or friction plate of the closing device stays under tension and can only be lifted with difficulty, despite prior venting. The reason for this is that the pressure plate of the tensioning device can only be lifted a limited distance from the tensioning wheel, as the entire apparatus is pressed with a strong force against the package by the completed tightening. As the venting path of the tensioning device is limited, the separating element, which has moved during the tensioning under the tensioning wheel in the direction of the tip of the approximately wedge-shaped opening between the upper and lower ends of the strap, does not disengage or disengage completely from the ends of the strap, that is, it ensures that these cannot disengage from the surfaces of the tensioning wheel or the pressure plate which are roughened by means of teeth or barbs.
In accordance with the present invention, provided is a device for tensioning and closing tightening straps which avoids these disadvantages and ensures a relaxation of the tightening straps relative to one another after producing a connection laterally next to these, even when only a limited venting path is available between the pressure plate and the tensioning wheel in the tensioning device.
This is accomplished by a tensioning device according to the present invention which includes an unblocking element which displaces the separating element during the lifting of the pressure plate from its relative position to the tensioning roller or to the pressure plate approximately parallel to the two ends of the strap. With the help of such an unblocking element, the separating element is necessarily displaced during the venting of the tensioning device and is moved from the position which it has taken during the tensioning of the two ends of the strap against each other. The displacement of the separating element parallel to the longitudinal direction of the tightening results in that a relatively small opening width between the tensioning wheel and the pressure plate during the venting of the tensioning device between the tensioning wheel and the separating element on the one hand, and this and the pressure plate on the other hand, produces sufficiently large gaps, and the ends of the straps leave their frictional connection to the tensioning wheel or the pressure plate. In a particularly advantageous manner, the separating element can be displaced from the unblocking element in the approximately wedge-shaped gap which forms during lifting of the pressure plate in a direction pointing away from the tip of the wedge gap or the connecting point of the ends of the strap, that is in a region, in which the ends of the strap have a greater distance from one another.
A tensioning device according to one aspect of the present invention can include an unblocking element which essentially consists of a spring element engaging the separating element, which spring element is under a spring pretension and which also draws or presses the separating element, which is also called hold-up wedge, during the venting of the pressure plate from the wedge-shaped gap between the ends of the strap away from the tip of the wedge gap or the weld seam between the ends of the strap. An embodiment of the invention, in which the unblocking element consists essentially of a release wedge cooperating with a gliding surface of the separating element is of particular advantage. During the lifting of the pressure plate the gliding surface of the separating element reaches the oblique part of the release wedge and displaces thereby the separating element automatically forward out of the approximately wedge-shaped gap between the ends of the strap when the tensioning device is vented. The separating element is advantageously arranged at a carrier shoe carrying the pressure plate, which is moved transversely to the longitudinal direction of the tightening strap during the venting of the tensioning device and thereby lifts the pressure plate and the separating element simultaneously from the tensioning roller.
In accordance with another aspect of the present invention, the tensioning device includes a separating element which is conveniently designed as a separating plate with a curved surface which is adapted to the radius of the tensioning roller, whereby a safe hold of the upper end of the strap between the tensioning wheel and the separating element is effected and correspondingly high tensioning forces can be achieved. The pressure plate is preferably arranged in a fixed manner at the carrier shoe, while the separating element is mounted approximately parallel to the ends of the strap at the carrier shoe in a moveable manner. For this, it can engage a longitudinal hole with play, which is formed at the carrier shoe with a lateral mounting end, and can be secured therein by at least one securing bolt engaging an arresting opening in the securing end.
In accordance to yet another aspect of the present invention, the tensioning device includes an unblocking element which is preferably adjustable by means of an adjusting device, whereby the adjusting device can for example consist essentially of a set screw with which the relative position of the release wedge can be changed, or the pretension of a spring element serving as the unblocking element can be changed.